The invention relates to a stator in particular of a housing-less electrical machine with liquid cooling, and to a manufacturing process for such a stator arrangement.
It has long been known to cool electrical machines such as electric motors or generators with a gaseous or liquid medium. Air is preferably used as the gaseous medium and water as the liquid medium. In the case of air cooling, the electrical machines are self-ventilated or externally ventilated.
In the case of liquid cooling, water is typically used as the cooling medium, which is conducted through metallic pipes such as through copper or steel pipes, for example. These pipes can be laid in meandering fashion through the stator of the electrical machine. For this purpose, the respective cooling pipes are connected at both end sides of the electrical machine to deflecting devices, such as U pipes, for example, or to a deflecting chamber. Furthermore, a cooling water inlet and a cooling water outlet also need to be provided. The heated cooling water is supplied to a heat exchanger or a radiator, via which the majority of the waste heat of the electrical machine can be dissipated further to the surrounding environment.
The stator of an electrical machine is conventionally in laminated form in order to minimize the eddy current losses resulting during the excitation. For this purpose, the stator is in the form of a laminate stack comprising a large number of thin electrical steel laminations with an axial stacking order. In order to cool the electrical machine, corresponding cutouts, preferably in the form of punched-out portions, are provided primarily in the lamination section of a stator electrical steel lamination. Once the laminate stack has been assembled, axially running cooling channels are produced, through which, for example, air can be conducted for cooling purposes.
In the case of liquid cooling of the electrical machine, metal pipes can be provided which are fitted into the channels resulting from the punching-out process, wherein the diameter of the usually circular metal pipes is intended to be slightly smaller than the diameter of the corresponding circular punched-out portions in the electrical steel lamination. The aim of this is to produce good heat transfer between the laminate stack and the cooling liquid.
One disadvantage in this case is the considerable degree of complexity involved with installation in order to introduce the cooling pipes into the stator, primarily in the case of axially relatively long electrical machines.
Liquid cooling is preferably used when electrical machines are intended to be operated close to their power limit, i.e. the thermal power loss to be dissipated is comparatively high. The electrical connection power of such electrical machines is typically more than 5 kW. Liquid-cooled electrical machines are additionally quieter during operation since no fans are needed. On the other hand, the technical complexity involved for liquid cooling is much greater than for air cooling.
Different housings are used for the electrical machines depending on the type of cooling, with the cooling means being provided in the housings. In the case of electrical machines without a housing, both cooling types can also be provided by suitable lamination cutting of the electrical steel laminations. Thus, in the case of liquid cooling, cooling pipes with a preferably circular cross section can be inserted into corresponding channels in the laminate stack.
The disadvantage here is the fact that a large number of pipe connections is required in the case of liquid cooling in order to join the numerous cooling pipe ends tightly in terms of hydraulics. This can take place in the case of copper pipes, for example, by means of a soldered joint or screw connection. The manufacture of such a cooling device is correspondingly involved.
In order to cool a housing-less electrical machine with water, cooling pipes, heat pipes or cool jets need to be passed through the laminate stack of the stator since the laminate stack on its own does not produce a sufficient sealing effect. This deficient sealing effect can result in considerable operational faults, in particular in the direction of the winding system of the electrical machine. An air gap is thus produced between the cooling pipe and the laminate stack, which air gap impairs the thermal connection between the cooling pipe and the stator.
The possibility of reducing the air gap between the cooling pipe and the laminate stack of the stator can be performed either by axial press-in operations of the cooling pipes into the cooling channels of the stator or else by virtue of the fact that this air gap is filled with thermally conductive paste or by impregnating resin in order to improve the thermal connection.
For example, DE 197 42 255 C1 has disclosed a housing-less three-phase machine with axially parallel coolant pipes which are arranged in the stator laminate stack. Since these coolant pipes are designed to be rigid, difficulties can arise when they are pushed into bores of the stator laminate stack, primarily since there is intended to be a comparatively small air gap between the cooling pipe and the stator laminate stack.
DE 101 03447 A1 has disclosed a cooled stator for an electrical machine, in which a corrugated metal tube is arranged in the cooling channels in order to facilitate fitting.
US 2004/0012272 A1 has disclosed an electrical machine in which metal pipes are pressed into half-open cooling channels on that side of the laminate stack which faces away from the winding system.
These previously known solutions are either extremely complex in terms of manufacturing technology and/or are comparatively ineffective thermally.